Proposals for composite containers have been in existance for a number of years. Generally, the composite container consists of an outer container that has some type of strength characteristics and an inner liner which is normally of a flexible plastic material that can be hermatically sealed. An example of an earlier version of a composite container is shown in U.S. Pat. No. 2,338,604.
Other examples of composite container constructions are disclosed in the following U.S. Pat. Nos.:
2,082,995; 3,285,461; 3,383,026; 3,620,399; 3,790,021; 4,141,466; and 4,169,540.
For many years, attempts have been made to substitute some type of package for the conventional metal container that is utilized for packaging of food products, such as vegetables and coffee. In the packaging or canning of vegetable products, it has been customary to provide a rigid metal container that is corrugated around the cylindrical peripheral intermediate portion to provide rigidity for the container and allow it to withstand crush pressures as well as resist collapsing during various phases of packaging and processing of the product therein. Conventionally, in the packaging of sanitary food products, the metal container must be internally lined to prevent any contamination of the product during processing and storage prior to ultimate use.
In the processing of food products, such as vegetables, it is standard practice to place raw vegetables into the open end of the container, supply a negative pressure to the product to remove all oxygen from the inside of a container and seal an end to the open ended container while the vacuum is being applied to the internal area of the container. After the container has been sealed, the container with the product therein is normally passed through some type of heating process wherein the product is heated for a short period of time in the range of at least 250.degree. F. During such heating, the product of course expands and the container has internal pressures applied thereto. However, upon cooling, after the finishing of the process, the food product again contracts and therefore the inside of the container again is at a negative pressure which the container must withstand without collapsing.
In packaging other products, such as coffee, the product is placed in a container, a vacuum is applied thereto and the container is sealed resulting in a vacuum inside the container which the container withstands without collapsing. Some other products are hot filled, sealed and then cooled which also results in a negative pressure in the container.
In the transportation of various articles, many times the articles are stacked in numerous cases upon each other which means that the lower container must be capable of resisting substantial crush pressure from the remaining containers supported thereon. It is also possible for the containers to be dropped and again the container must withstand the forces encountered without collapsing.
Numerous attempts have been made to substitute various types of less expensive and less rigid packages particularly for food products and an example that has been dealt with for a number of years is what is commonly referred to as a "retort" pouch. In order to meet the various governmental requirements, the typical pouch construction consists of a layer of polypropylene attached through an adhesive to an aluminum foil layer with a further polyester layer adhesively secured to the opposite surface of the foil. The aluminum foil provides the oxygen barrier resistance that is required for packaging such products while the polypropylene is utilized to provide chemical inertness for the product and the polyester layer produces the necessary mechanical strength for the pouch.
One of the main problems with a pouch of this type, when used for packaging food products, is the fact that the relatively flexible package slows the filling speeds of the filling line and therefore, increases the cost thereof. For example, pouches of this type require a special system that will provide a mechanical support for the pouch during the heating or processing operation for the contents.
A further problem that has been encountered with the pouch type package is the fact that the pouch does not have sufficient rigidity to be self-supporting without collapsing during shipment and display. Thus, most pouches that are utilized for packaging, particularly food products, are, of necessity, placed in an outer cardboard or other carton for shipment and display purposes, adding to the overall cost of the package.